1. Field of the Invention
This invention relates to a valve assembly and in particular to an improved butterfly valve assembly for controlling fluid flow therethrough, wherein such valve assembly is particularly adapted to be used on a railway tank car as a bottom operable lading valve.
2. Description of Prior Art
It is known in the art to provide a valve assembly for a railway tank car which is operable from the bottom of such tank car. Examples of such a valve assembly are disclosed in copending U.S. patent application Ser. No. 459,462; and, such application also discloses the use of a butterfly valve assembly. U.S. Pat. Nos. 4,016,907 and 4,394,002 also disclose bottom operable butterfly valves for railway tank cars.
However, the Association of American Railroads (AAR) and the Department of Transportation (DOT) have railway tank car regulations which require that projections extending in excess of 1 inch below the bottom of the tank of such a car must be protected by a skid, or if such a projection is part of a valve assembly associated with the tank car it must be capable of being sheared away without affecting the integrity of such valve assembly. In instances where a skid is provided this skid must be in the form of a ramp having a longitudinal dimension along the bottom of the tank which is three times the dimension projecting downwardly from such bottom.
It is important in providing a valve assembly for a tank car such as a railway tank car to provide a valve assembly which will not tend to open during normal usage thereof and wherein such normal usage includes continuous and substantial vibration of the valve assembly as its associated railway tank car is moved along an associated track. In an effort to prevent opening of a butterfly valve used on a railway tank car the above-mentioned U.S. Pat. No. 4,016,907 discloses a butterfly valve assembly which has a complex locking mechanism which is provided for locking the actuating stem assembly used to open and close a closure structure which comprises such valve assembly.
It will also be appreciated that in many tank cars or other applications using a butterfly valve a highly viscous fluid such as, heavy petroleum, molasses, sulphur, or the like is controlled by such valve. In these instances it is desirable and often necessary to heat various portions of the valve to promote flow of the highly viscous fluid therethrough and/or to assure satisfactory operation of the valve seals. In other applications it is desirable to cool such various portions of the valve to assure proper fluid flow therethrough and/or prevent degradation of valve components such as valve seals.
It is known in the art to provide heat exchange means for heating and/or cooling selected portions of a valve assembly or components associated therewith. For example, the above-mentioned U.S. Pat. No. 4,394,002 discloses provision of spaces in a mounting flange for a butterfly valve wherein such spaces are used to supply steam to the flange for heating purposes. Similarly, U.S. patent application Ser. No. 473,555 discloses a butterfly valve construction which has heat exchange means in the valve body structure thereof and/or in the closure structure thereof.
However, each butterfly valve proposed heretofore and particularly each butterfly valve proposed for use as a lading valve for a tank car is deficient in at least two respects. The first deficiency is that the locking means provided to lock the closure structure of such valve in its closed position to prevent inadvertent opening thereof during normal usage does not provide a positive locking action or is too complex and expensive. The second deficiency is that the locking means is often used with an associated actuating shaft for the closure structure and such shaft is often drastically reduced in cross section to provide a locking means whereby the strength of the shaft becomes marginal and is prone to premature failure. In addition, each butterfly valve proposed heretofore which has heat exchange means associated therewith is deficient because it has at least portions thereof which are not heated or cooled in an optimum manner.